I played off and on ever since the end of Polaris and have really gotten back into the game and would like to have better gear for my main character but Rattlebones's chances to drop the Exalteds seems to be nonexistant, whereas before the dungeons seemed really common to be dropped
Rattlebones is a one shot kill, so pretty easy to do a ton of runs to get the duels. There are other bosses that drop them along with the other dungeons, such as jade oni and krokopatra.